Diagnosis and Management of Gastrointestinal Neuroendocrine Neoplasms.

The latest WHO classification cleanly divides gastrointestinal neuroendocrine neoplasms into neuroendocrine tumor (NET; well-differentiated, any grade) and neuroendocrine carcinoma (NEC; poorly differentiated, high-grade by definition), along with mixed neuroendocrine-non-neuroendocrine neoplasms. NECs are always aggressive, with multiple mutations; they are treated with chemotherapy. NETs have widely different presentations, behavior, and management depending on site of origin. Esophageal examples are vanishingly rare. Most gastric and appendiceal tumors are indolent, as are many colonic and rectal tumors. The duodenum is home to some unusual variants of NET, and jejunal/ileal NETs frequently metastasize, which impacts their staging and clinical management.